Not sure about that. The Bluefin Tuna usually swim oceans and they are fast. These swam around a warm shallow bay in the Mediterranean - about 10 to 15 metres deep, very slowly. Also I could only ever see two fins each above the water. I thought they may be spearfish, a type of swordfish. Possible? Bendigo

I'm just wondering if they could have been young Marlin playing near the surface. The tip of the tail is the right shape in the second picture. Also the proportions and spacings look right from the dorsal to the caudal fin, for a fish around 1.5 meters in length.